Because telecommunication systems are handling increasing quantities of data traffic, optics-based equipment and solutions are gaining momentum. Optical fibers are now commonly used to interconnect systems that require a large network bandwidth over long distances, with a relatively low cost compared to copper cables. As systems grow and optical solutions become more affordable, system designers are also beginning to use optical components and interconnections for short-range communications within systems as well as for long-range connections between systems.
In large-capacity systems, it is common to use a system design that uses an equipment “chassis” as the form factor. An equipment chassis is often called a “subrack,” or “card cage,” or “subrack card cage.” In the remainder of this document, the term “subrack” is used, although it should be understood that this term is interchangeable with “chassis” and “card cage.”
Typically, a certain number of printed circuit board (PCB) “blades” can be slid into and plugged into a subrack. Further, several such subracks can be installed in a rack, allowing system designers to build a scalable system. In order to allow the different blades to communicate with one another, each blade needs to be connected to a backplane, which is responsible for carrying the communication signals between the blades.
Typically, a backplane is passive, i.e., it does not require any external electrical power, and is built in such a way that copper traces can be used to exchange information between the blades. FIG. 1 shows an example subrack 100, which can support several cards or blades that are interconnected together through the backplane 110. Backplane 110 has several connectors 120 for connecting each card to it and thus to one another.
In many systems, the backplane is designed to support a star, a dual-star, a dual-dual-star or a fully-connected network topology. Depending on the network topology selected, more or fewer copper traces might be required on the backplane. As the number of traces increase, e.g., in the case of a fully-connected network topology, there is often a need to develop a multiple-layer backplane to account for all the traces required to interconnect all the blades. Common problems with copper-based backplane are related to the facts that copper interconnects require a lot of energy, are sensitive to interference, and offer a limited bandwidth capacity. In practice, this means that several parallel traces might be required to fulfill the bandwidth requirement for a given interconnect between two slots. FIGS. 2 and 3 show different interconnect topologies that are often incorporated into backplanes, namely the dual-dual star topology and the fully connected network topology, respectively.
To simplify the design of backplanes, system designers are increasingly considering the use of optical interconnects. In fact, optics-based solutions offer a much higher bandwidth per trace/interconnect, and are not sensitive to electro-magnetic interference. Both of these qualities simplify the development of backplanes. As optical-based technologies become the technology of choice for the future, copper backplanes will be gradually replaced by optical backplanes.
One example of an optical backplane is illustrated in FIG. 4. Basically, an optical backplane can be seen as a group of optical fiber cables interconnected together in order to produce a network topology. In the example backplane 400 shown in FIG. 4, each of the connectors 410 and 420 includes multiple fiber ends, e.g., eight fibers per connector. In this configuration, the eight fibers extending from a connector 410 on the left-hand side of backplane 400 are distributed to the eight connectors 420 on the right-hand side of backplane 400. This configuration is typically referred to as an optical shuffle. When such an optical shuffle is installed on the back of a subrack in order to interconnect several subrack cards, it is referred to as an optical backplane. Note that it is also possible to integrate this same interconnection configuration (or others) into a backplane circuit board. Also note that in a subrack, the co-existence of a copper and an optical backplane is possible.
One or more optical shuffles can be packaged in a box, typically referred to as an optical shuffle box. An optical shuffle box can be used to interconnect several components of one or more systems. One difference between an optical backplane and an optical shuffle box is that the optical shuffle is not limited to interconnect the cards of a single subrack, nor is it limited to the use of backplane connectors, e.g., blind-mate connectors. One example of an optical shuffle box is shown in FIG. 5, where shuffle box 500 includes a large number of optical connectors 510 on both the front and back sides of the shuffle box 500. Once again, each of the optical connectors 510 may terminate several optical fibers, such as 24 fibers per connector. Optical cables are used to connect the optical connectors 510 to connectors on other subracks in the system.
With the continued growth of telecommunications and increasing requirements for flexibility in terms of interconnection specifications, the option of replacing copper backplanes with optical backplanes continues to become more attractive. However, the increasing size and complexity of these systems also tend to make system maintenance and system changes more difficult. Accordingly, improved solutions for optical interconnect systems are needed.